iTunes 11 isn't opening my audiobook downloads. Why??

I have just downloaded the new update for iTunes (which I hate doing becuase its always different and takes a while to get used to) and now it won't open new audiobook files from Audible.com. Audible is designed to work with iTunes and I've never had any problems with it before. I have followed all of the instructions on the Audible troubleshooting pages but iTunes still won't acknowledge my new downloads. I don't understand and its really annoying. I wish I hadn't downloaded the stupid iTunes update in the first place. My old iTunes worked fine. Has anyone else had this problem? How do you overcome it?